A methacrylic resin has excellent transparency, weather resistance, moldability and processability and has been widely used in automobile parts, lighting goods, various panels and the like. However, generally, its use has been narrowed owing to its inadequate impact resistance.
Accordingly, a method of improving impact resistance of a hard resin such as methacrylic resin by adding a multilayered graft copolymer having a basic structure of three-layer structure of a specific hard-soft-hard construction to improve impact resistance of the methacrylic resin has been proposed (for example, refer to Patent Document 1). However, improvement by this method is not sufficient, though impact resistance can be improved to some extent. Further, when impact resistance of a resin is improved by such an impact resistance modifier, the resin is liable to suffer whitening by impact. Therefore, improvement of not only impact resistance but also resistance to whitening by impact has been demanded.
A method of improving resistance to whitening by impact while maintaining impact resistance by using a multilayered acrylic polymer having a specific structure has been proposed (for example, refer to Patent Document 2). However, a further improvement of impact resistance has been demanded, though resistance to whitening by impact is improved.
Although it is possible to realize higher impact resistance or resistance to whitening by impact if a large amount of an impact resistance modifier such as multilayered acrylic polymer mentioned above is used in a methacrylic resin composition, such a methacrylic resin composition has a low usefulness because its hardness is lowered. Further, it is more preferable to use smaller amount of such an impact resistance modifier as that mentioned above because the more the impact resistance modifier is used, the higher the production cost becomes. Therefore, an impact resistance modifier which can effectively improve impact resistance and resistance to whitening by impact with a small amount of its use and a resin composition in which it is used have been expected.
Patent Document 1: Japanese Patent Publication No. Sho55-27,576
Patent Document 2: Japanese Patent Application Laid-Open No. Hei10-338,723
Non-Patent Document 1: POLYMER HANDBOOK THIRD EDITION